This application claims benefit of Japanese Patent Application No. 2003-098706 filed on Apr. 2, 2003, the contents of which are incorporated by the reference.
The present invention relates to radio network systems, radio base stations and radio mobile terminal agent processing methods used for such systems and stations and, more particularly, to radio LAN (Local Area Network) systems connected to internet or intranet and utilizing data communication (particularly real-time communication dealing with voice and motion picture images) on the basis of IP (Internet Protocol).
With the spread of radio communication techniques, such radio mobile terminals as portable telephone set, PHS (personal handy-phone system, PDA (personal digital assistant) and small-size note-type personal computer, have become widely used. Such radio mobile terminals can be connected to internet via access points without use of any communication cable and also perform data communication with other data processing units on LAN, WAN (Wide Area Network) and PAN (Personal Area Network).
Recently, concerning this type of data communication, radio LAN communication equipment called hot-spots are installed in various places such as station premises and coffee shops. By providing a radio function to them, these radio mobile terminals permit their connection to internet via the hot-spots when their owners are out of home, permit reading home pages and transmission and reception of electronic mails.
Also, by using such a radio communication system, enterprises, shops and offices can reduce man-hours and expenditures for laying the communication cable such as LAN cable a fresh with a floor change. Furthermore, the system easily and quickly permits communication without need of any process of directly connecting terminals, the owners of which are frequently moved in departments and buildings, to a fixed cable.
In the above radio communication system, the radio mobile terminals are wirelessly connected to the radio base station as access point, and therefore the power supply line is usually not directly coupled to the radio mobile terminals. In other words, as a rule the radio mobile terminals are battery driven, and can only exceptionally use a charging device such as charging stand or a power supply adapter when they are located near a desk or like fixed place. Accordingly, it is heretofore been contrived to reduce the power consumption of the radio mobile terminals so as to be able to use the battery for longer time or reduce the power consumption to reduce the battery with as much as possible.
Among the power consumption reducing methods is one, which permits power consumption reduction when the radio mobile terminals are found outside the permissible communication range (first technique, see Literature 1: Japanese Patent Laid-open No. 2002-208887, pages 4-6 and FIG. 1, for instance). In this method, however, a radio mobile terminal located outside the permissible communication range, is not only unable to execute communication, but also execute channel scan for searching a waiting channel, thus leading to an increase of the degree of battery consumption. Accordingly, when a predetermined time has been passed with the radio mobile terminal found outside the range, power is provisionally cut off, thus preventing power consumption in the state that the radio mobile terminal is unable to execute communication.
As a different power consumption reducing method has been proposed one, in which the power consumption is saved by partly changing the functions of the circuit device of the radio mobile terminal (second technique, see Literature 2: Japanese Patent Laid-open No. 2000-278165, pages 8-14 and FIG. 1, for instance). This second technique deals with the reduction of power consumption in portable telephone sets in CDMA (Code Division Multiple Access) system.
Specifically, in the second technique different A/D (analog/digital) conversion bit numbers are set in the A/D converter at the time waiting speech and at time of communication such that the A/D bit number at the speech waiting time is less than that at the communication time, thereby reducing the power consumption in the A/D converter and a dispersion process computer and thus reducing the power consumption at the speech waiting time.
As a further power consumption reducing method has been proposed one, in which a radio part in a radio mobile terminal is on-off controlled during waiting time thereof, thereby saving the power consumption at the “off” time (third technique, see literature 3: Japanese Patent Laid-open No. 2002-118874, pages 4-6 and FIG. 1, for instance). In this third technique, when the user starts an on-off setting function of the radio part during the waiting time, the radio mobile terminal checks whether the radio part has been started.
In the duty service time, the user monitors whether an operation of stopping the radio part has been done. When the stopping operation has been performed, the user reports to the network that the radio part will be stopped, and stops the radio part. In this state, the speech waiting state is restored. When the stopping operation has not been done, like the above case the speech waiting state is restored with the radio part held without being stopped.
When the radio part is not in the duty service time at the time of the start of the on-off setting function in the reading part by the user, the user monitors whether the starting operation will be performed. When the user executes the starting operation, the radio part is started, and reports to the network that the radio part has been started. In this state, the speech waiting state is restored. Unless the user does not perform the radio part starting operation, the speech waiting state is restored.
In this third technique, since the radio mobile terminal user manually on-off controls the radio part, problems that the operation is cumbersome and that erroneous operation is liable are posed. A technique in which such radio part on-off operation is to be done automatically, has also been proposed (fourth technique, see Literature 4: Japanese Patent Laid-open No. Hei 7-131404, pages 4-5 and FIG. 2, for instance).
In this fourth technique, however, although a power saving effect is obtainable for a clearly predetermined scheduled non-use time, no power saving is made for a relatively long time such as a business time zone in an enterprise, in which the use of radio mobile terminal is presumed, and during such time no power saving effect can be obtained.
In this fourth technique, however, although a power saving effect is obtainable for a preliminary clearly predetermined non-use schedule time, no power saving is made for business time zones in enterprises or like relatively long time, during which the use of radio mobile terminals is presumed. Therefore, no power saving can be expected during such time.
Accordingly, as a technique different from the above techniques, a radio communication system, which seeks power saving, is in practical use. This radio communication system is called radio LAN system, and each radio mobile terminal can select a power-saving mode for saving power consumption and a normal mode. Each radio mobile terminal is adapted to report to the radio base station side whether or not the power-saving mode is to be used.
In the radio LAN system utilizing radio as transfer medium, each radio mobile terminal utilizes the power-saving mode by intermittently receiving announcement data (or beacon) from the radio base station. Specifically, when the radio mobile terminal is set to be in the power-saving mode, it reports to the radio base station by using a predetermined protocol that it is operating in the power-saving mode, and executes the operation of intermittently receiving announcement data.
The radio base station, receiving the report from the radio mobile terminal, buffers (stores) packets addressed to the radio mobile terminal operating in the power-saving mode in the memory of the own station, and report to the radio mobile terminal by using traffic display map (TIM) of announcement data that it has buffered packets addressed to the radio mobile terminal.
The radio mobile terminal receiving the announcement data from the radio base station, confirms the traffic display map and recognizes that the packets to addressed to itself have been buffered, whereupon it transmits a control message urging the distribution to the radio base station. The radio base station, receiving the control message urging the distribution from the radio mobile station, executes the operation of transmitting the buffered packets to the radio mobile terminal. The broadcast packets to all the radio mobile terminals belonging to the radio base station are transmitted after announcement data with DTIM (distribution traffic display message).
In the above prior art radio LAN system, the radio base station has to provisionally buffer and accumulate packets addressed to each radio mobile terminal operating in the power-saving mode as shown above in the memory in the own station until receiving a control packet urging the distribution sent out from the radio mobile terminal.
Also, in the case of this operation, in the real-time communication in which the radio mobile terminal has to play each packet as soon as it receives the packet, packets are provisionally accumulated in the radio base station and distributed in response to a poring from the radio mobile terminal in the next reception cycle thereof. Therefore, the packets are greatly delayed, leading to trouble occurrence in the playback.
Furthermore, in the prior art LAN system, from the consideration of the power saving in each radio mobile terminal, a broadcast packet is transmitted after announcement data with distribution traffic display message. Therefore, for receiving the broadcast packet, the radio mobile terminal should always receive announcement data with distribution traffic display message. This means that long cycle intermittent reception for realizing the power saving can no longer be made.
A physical address inquiry protocol for solving the physical address of the radio mobile terminal, is transmitted in the broadcast packet. Therefore, a radio mobile terminal which does not receive any announcement data with distribution traffic display message can not solve the physical address.
Still further, in the prior art radio LAN system, when the radio mobile terminal increases the intermittent reception cycle for reducing the power consumption, a delay is caused in the packet reception in the connection call process, thus giving rise to such problem as it is no longer possible to make a connection upon time-out in the opposite side terminal.
Yet further, in the prior art radio LAN system, when the radio mobile terminal is in the power-saving mode, the above real-time communication packet generation cycle is relatively shorter than the intermittent reception cycle in the radio mobile terminal, and this leads to the problem of overflow in the buffer in the radio base station.
Further, in the prior art radio LAN system, when a large number of radio mobile terminals operating in the power-saving mode come to belong to the radio base station, a very large number of memories are required for accumulating packets addressed to the radio mobile terminals.
Further, in the prior art radio LAN system, when a physical address solution protocol appears on the network, because of the broadcast packet, a problem arises that the limited band is consumed by the sending of the packet to the radio line irrespective of presence or absence of address to any radio mobile terminal.